This invention relates to borescope or endoscope of the type in which a miniature video camera is mounted at a distal viewing head of an elongated insertion tube. The invention is more particularly concerned with an improved laparoscope in which illumination for the miniature video camera is supplied from a low-wattage but high-efficiency lamp and thence through a light conduit to the tip of the laparoscope probe tube.
Recently, the need and preference for less invasive surgical techniques has increased the interest in the use of video instruments for surgical applications, and in video-based procedures with minimal intervention in the patient. An example of a minimally invasive video instrument is a laparoscope for performing surgery in the abdominal cavity, where the instrument is inserted through a small incision. Other probes are provided for diagnosis of medical conditions in the colon or in the gastro-enteric tract. Small probes can also be used in eye surgery. Further examples are found in industrial probes, i.e., borescopes, for inspection of equipment such as boilers or steam generators, or jet engine rotors where non-destructive penetration of the equipment is necessary. In each case the tissues or parts to be investigated may be quite sensitive to heat; thus if infrared or heat is produced with the light from the instrument's light box, inspection can injure or damage the target.
It is also desirable for the laparoscope to operate at low power consumption rates, for example, so that the unit can be constructed compactly and of light weight, and also so that the laparoscope can be made battery powered and portable, e.g., for veterinary purposes.
However, until now suitable illumination was possible only with high wattage, high pressure xenon arc lamps. These produce a large amount of waste heat and their energy cannot be focussed down onto a small spot to enter a fiber optic bundle or other light conduit. The heat is not only wasted but it can also be dangerous, as numerous cases of abdominal burns and surgical drape ignitions have been reported.
A video laparoscope with a light source based on small, low-power metal halide discharge lamp is described in copending patent application Ser. No. 07/780,762, filed Oct. 22, 1991, now U.S. Pat. No. 5,331,950, and having a common assignee. As described in that patent application, a laparoscope or other similar probe has a miniature video camera that incorporates a miniature electronic imager and a lens assembly which are disposed either at the distal tip or at a proximal end of an insertion tube. For insertion tubes of about 5 mm or larger, the camera can be distally mounted. For very slim insertion tubes, the camera can be proximally mounted, with a relay lens system being contained in the insertion tube. The insertion tube can be rigid or can have its tip portion articulatable. The small video camera can be incorporated in an add-on camera attachment for laparascopes having a proximal viewing port.
Disposing the camera at the distal tip of the laparoscope insertion tube reduces the amount of focussing and relay lenses to be carried in the tube. This means less light is lost in the lens system, so the amount of optical fiber bundle needed for illumination, is reduced which also permits the insertion tube to be made smaller.
The insertion tube proximal end is coupled through a flexible cable or umbilical to a connector module that plugs into a socket in a processor unit. A video cable that extends through the insertion tube and umbilical has terminals in the connector module that supply the video signal from the miniature camera to electronic circuitry in the processor, which supplies a suitable signal to a full color or monochrome monitor. An image of a target area, such as a tissue within a patient's body cavity, can be viewed on the monitor.
Also within the processor is a high illuminance, but low-wattage light source in the form of one or more metal halide discharge lamps. These can preferably be of the type described in Copending Patent Application Ser. Nos. 07/484,166, filed Feb. 23, 1990, now U.S. Pat. No. 5,144,201; 07/636,742, 07/636,743, and 07/636,744, each filed Dec. 31, 1990, now U.S. Pat. Nos. 5,117,154, 5,083,059, 5,138,228, respectively, and which have an assignee in common herewith. The lamp typically operates at a power of about 20 watts dc, and has an efficacy of at least 35 lumens per watt. The light produced, which can be controlled by the selection of salts employed, the dosage of mercury, and mechanical structure of the lamps, has an emission spectrum in the visible band, with very little radiation produced in the infrared band. Also, the arc gap of this lamp is small, which produces a small spot of light when focused onto the fiber optic bundle used for illumination. The small spot size allows almost all the light energy to be directed into the proximal end of a very small fiber bundle. The smaller illumination bundle permits the insertion tube to be made much smaller than was previously possible while still delivering plenty of light to the target area. Also, because small optical fiber bundles can be used, the probe can incorporate redundant optical fiber bundles, which can each be associated with a respective light source. Moreover, because the lamp operates at low power (e.g. 20 watts), producing limited infrared radiation, and with virtually all the light being focused onto the fiber optic bundle, the light source can be made much more compact, and the lamp power supply can be much smaller. The light incident on the target consists substantially only of visible light, with very little radiant heat. This permits the operator to view and examine tissues for extended intervals without danger of tissue damage or the ignition of surgical drapes.